This site is operated by a business or businesses owned by Informa PLC and all copyright resides with them. Informa PLC's registered office is 5 Howick Place, London SW1P 1WG. Registered in England and Wales. Number 8860726.

No more silver bullets in the herbicide gun

Roy Roberson | Mar 15, 2006

Going on 20 years ago, I stopped in at the Tennessee Valley Research Station in Belle Mina, Ala. to visit with then Superintendent of the facility, W.B. “Dub” Webster. It was routine procedure to visit the day before a big field day to get an update on new research findings in order to help the ag media better report these research results.

On this day, I asked the usual questions about soybean and cotton research and got Dub's usual thorough evaluations of what would be shown the next day. “Is there anything new and exciting,” I asked Dub. “Yea, he said, but if you tell anybody about it, we'll have to chop you up and feed you to the hogs.”

Laughing, we climbed into his pickup and headed to the back side of the research farm. “I want to show you three soybean weed plots — tell me what you think about ‘em,” he grinned.

Looking at three four-row plots, I surmised the one on the right is the check plot — has more weeds than soybeans, I noted. The middle plot is clean as the back of your hand — must be the Cadillac treatment, I added. The third plot was nothing more than a few blackened stems with a few dead leaves spread around under them. It looks like somebody forgot to change the sprayer tank and sprayed the beans with paraquat or glyphosate on that last plot, I said, thinking that was too easy for a journalist to figure out.

“Well, Dub said, that plot on the left was sprayed with Roundup.” I jokingly asked if it were real smart to use tax dollars to figure out that glyphosate will kill 10-12 inch soybeans. He put his hand on my shoulder and with an atypical serious look on his face said, “son, both of those plots were sprayed with Roundup.”

After getting a rudimentary explanation of gene transfer technology and my first introduction to glyphosate-resistant herbicides, I became a fan of this process. Though I couldn't write anything about it at the time because of a contractual agreement between Auburn University and Monsanto, I knew it would be big news in the ag press for a long time to come.

If anyone doubts the economic importance of glyphosate resistant technology to farmers, consider these numbers from just one crop — soybeans. Each year this technology saves soybean farmers $186 million in the cost of herbicides, another $62 million per year in fuel costs, and over 22 pounds per acre of active ingredients in herbicides.

This technology, along with the Boll Weevil Eradication Program, has been the driving factors in the return of cotton as king throughout the Southeast. It has allowed thousands of farmers nationwide to switch to more economical and conservation-minded reduced-tillage systems, and eliminated the risk of millions of pounds of chemicals getting into our water supply.

There is a downside! And, as I predicted glyphosate resistant herbicides are still big news in the ag press.

In recent years glyphosate resistant horse nettle species have been documented and well-chronicled in this and other farm magazines. Though the spread in Tennessee was rapid, creating concerns among weed scientists, this weed has never been a major pest in the Southeast, so it got little attention here.

In the summer of 2005, University of Georgia researchers found glyphosate resistant Palmer amaranth, commonly called pigweed. Subsequently, Alan York at North Carolina State University, one of the nation's premier weed scientists, concluded resistant pigweed likely will be found in the Carolinas. “This puts glyphosate resistance in a whole new ballgame in the Southeast,” York told a large audience of farmers at the recent Beltwide Cotton Conference.

I've now seen in several meetings pictures from the University of Georgia tests in which nearly two gallons of a glyphosate-containing herbicide was applied to Palmer amaranth. If there was any damage to the weed, it was not evident from the pictures. Alan York showed similar pictures during his Beltwide presentation, noting these images “should scare cotton farmers to death.”

Though Palmer is only one of many species of pigweed that have plagued farmers for years and provided long careers for weed scientists, most pigweed species have shown an uncanny ability to develop resistance to herbicides.

In the past the answer to resistance problems, for all weed species, has been to load a new bullet in the gun and fire away. When weeds developed resistance to that herbicide, add a new one and spray away. One of the sad realities of the success of glyphosate resistant technology is that it has sapped the profit and squelched the desire of herbicide manufacturing companies to develop new chemistry. As Alan York sadly proclaimed at the Beltwide Cotton Conference — there are no new herbicides in the pipeline.

Chris Main, a weed scientist at Clemson University's Pee Dee Research Centers says, conservatively, growers are looking at 8-10 years before any new herbicide technology will make it to the farm. At a recent South Carolina Soybean Production Meeting, Main urged growers to diversify away from glyphosate, but to use available alternatives wisely.

While there may not be new chemistry to control pigweed, there are plenty of highly successful, well-documented herbicides to control this and other weed pests. The key is to use these materials wisely. Herbicide resistance is not new, but with over 90 percent of soybeans and cotton planted in glyphosate resistant varieties, the risks have never been this high.

Management and knowledge in a glyphosate resistant world will be critical for survival. Growers should know which families of herbicides are available for all crops in a rotation. Knowledge of mode of action of these materials is critical to development of a herbicide resistance management program.

Short-term, such programs will likely cost more money. Long-term they may be the only salvation. And, though it may be heresy to say, in some cases a return to conventional-tillage may be a necessary part of herbicide resistance management programs.

Glyphosate resistance management programs either are available, or will be soon from crop specialist and/or weed scientists in every Southeastern state. These programs vary from crop to crop and state to state, and the combinations would likely fill this magazine. The important message is to find one that works in your operation and use it.

If there was ever a time to ‘hug your favorite weed scientist’ this is probably it.